As the demand for integrated circuits with ever-shrinking device features continues to increase, the need for improved illumination sources used for inspection of these ever-shrinking devices continues to grow. One such illumination source includes a laser-sustained plasma source. Laser-sustained plasma light sources (LSPs) are capable of producing high-power broadband light. Laser-sustained light sources operate by focusing laser radiation into a gas volume in order to excite the gas, such as argon, xenon, mercury and the like, into a plasma state, which is capable of emitting light. This effect is typically referred to as “pumping” the plasma. In order to contain the gas used to generate the plasma, an implementing plasma cell requires a “bulb,” which is configured to contain the gas species as well as the generated plasma.
A typical laser sustained plasma light source may be maintained utilizing an infrared laser pump having a beam power on the order of several kilowatts. The laser beam from the given laser-based illumination source is then focused into a volume of a low or medium pressure gas in a plasma cell. The absorption of laser power by the plasma then generates and sustains the plasma (e.g., 12K-14K plasma). Typically, a plasma cell includes a pair of electrodes used to initiate plasma generation in the given plasma cell. For example, the electrodes of a given plasma cell may produce a discharge arc or corona discharge suitable for initiating plasma generation within the given plasma cell.
As pumping powers continue to increase and plasmas become larger and hotter, thermal management in the glass cells becomes increasingly difficult. In a general sense, plasma cools down by several mechanisms, including radiation, convection, and the like. In turn, the cooling of the plasma can heat regions of the gas cell. In addition, the plasma also includes several mechanisms for heating the electrodes, which, in turn, radiatively or conductively heat the glass bulb of the plasma cell.
In the event the glass enclosure of the plasma cell reaches temperatures in excess of the softening point of the glass wall of the bulb of the plasma cell, then the cell is at risk of rupturing during operation (or after cooling). Therefore, it would be desirable to provide a plasma cell that corrects the deficiencies identified in the prior art.